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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

428                                ALASKAN GLACIER STUDIES
abandoned channel of this series heads in the air just west of Miles Glacier station, proving that the Copper River has undercut its south bank since this small stream channel was abandoned.
History of Oscillations of Miles Glacier—Advance Before 1840. Passing over the early stage when Miles Glacier was a tributary of a great Copper River Glacier, and the legendary stage when Miles and Childs Glaciers are supposed to have coalesced, with Copper River flowing underneath, the first stage of which we have knowledge is the expansion to the bulb glacier condition some time before 1840. It is quite possible that this expansion was preceded by one of shrinkage of Miles Glacier back within its mountain valley, and that it expanded into a trunk valley which was free from ice. The asymmetrical shape of the bulb suggests that Childs Glacier also had an expanded bulb, for the Miles bulb spread 2£ miles up the main valley and, so far as we know, only a fifth as far down Copper River valley, forming a striking contrast with the far more symmetrical bulb of Allen Glacier (Map 9).
We know nothing specific as to the date of this expansion to the present bulb form excepting that (a) Abercrombie's photographs prove that it took place before 1884, (b) Grewingk's description (p. 416) suggests that it took place long enough before 1850 for vegetation to grow on the ice, and (c) the age of trees growing on the outwash plain pushes the date back to some time previous to 1840. It may have been much earlier.
Slight Recession During the Eighties. Maintenance of an advanced position rather than pronounced recession is the impressive feature of the history of Miles Glacier during the time of the visits by Abercrombie and Allen. The northern portion of Miles Glacier bulb has retreated practically none in over 70 years; and the southern portion also maintained its advanced position for a time, the site of the lake basin being largely filled with glacier ice until very recently.
Abercrombie's mention of a lake basin shows that there had been some recession of the southern part of the glacier by 1884, and one of his photographs,1 taken from a point on the western terminal moraine of Miles Glacier, south of Grinnell Glacier, proves that the ice cliff had retreated to the point where the largest channel of Copper River now enters the lake. This position of the ice front represents over a mile of eastward recession from the expanded edge of the bulb at the southern end of Abercrombie Rapids. The great waves in the stream in the foreground of the same photograph show that a main channel of Copper River flowed down Chinaman Slough as recently as 1884. That the southern margin of Miles Glacier was not severely crevassed is indicated by the fact that Abercrombie traveled 8 miles upon its surface in August, 1884, being turned back by the crevasses in the middle of the glacier after traveling up its southern border.
In 1885 the front of Miles Glacier still filled the greater part of the present lake basin, as is indicated by Allen's descriptions, one of which includes the specific statement8 that "the most southerly point of the . . . (Miles Glacier) is 1 mile or less from the most northerly point of the . . . (Childs Glacier)."
It is clear, therefore, that while there was slight recession of the southern portion of the Miles Glacier bulb during the eighties, it did not uncover a significant part of the present lake basin. A comparison of Abercrombie's 1884 photograph of the northern portion of the bulb with our photograph from the same site shows practically no change in the 20
» Reproduced by H. T. Allen in Narratives of Explorations in Alaska, Washington, 1900, picture facing p. 426. > Allen, H. T., in Narratives of Explorations in Alaska, Washington, 1900, p. 486.